Due to the widespread use of computer, software and network, it has become possible to accelerate and share information processing. Fundamentally, digitization of information is suited for storage, accumulation, retrieval, etc. of information, whereas a paper medium is suited for display (particularly viewability) and transfer of information. It is therefore a present state that as digitization of information progresses, the consumption of paper is increasing. On the other hand, reduction of energy consumption represented by CO2 emission is an urgent need in various fields. If a paper medium which is used for temporary display or transfer of information can be recycled, a great contribution can be made to the reduction of energy consumption. There is a method in which a color is developed and erased by heating using a reversible heat-sensitive recording medium. However, in this method, a color-forming composition is present on a recording medium, and therefore, the method has a disadvantage that a common paper medium cannot be used. There is also known to produce an erasable toner by a pulverization method. However, the erasable toner has a disadvantage that in a process of melt-kneading components such as a color-forming agent, a color-developing agent and a decoloring agent, the components are reacted with each other, so that the density of the developed color is decreased and also a decoloring reaction rate is decreased. As a production method other than the kneading pulverization method, a production, method employing a wet process in which a toner is obtained by aggregating and fusing fine particles of an erasable color material and fine particles of a binder resin, etc. in an aqueous medium has also been proposed. According to this method, it is possible to mix the fine particles of the erasable color material with the binder resin, etc. to effect coalescence without being subjected to mechanical shearing or high thermal history by melt-kneading. However, in this method, it is difficult to completely incorporate the fine particles of the color material in a toner, and this method has been found to provide a problem that the fine particles of the color material released from the toner remain in the toner as fine powder to cause an image defect such as fogging. This tendency is particularly pronounced when the fine particles of the color material are microencapsulated.
On the other hand, it has been proposed that by crosslinking a toner resin using a reactive polymer, the fixability, thermal characteristics and mechanical characteristics of a toner are mainly improved.